PARENT SESSION
1:30 PM to 3:30 PM
Wednesday, April 24, 2002
Poster Session 26 Apoptosis
Room: Nevada Exhibition Center
(P31-306) TGF-Beta1 mediates apoptosis and p53 response in irradiated mammary gland.
Barcellos-Hoff, M.*,1, Ewan, Kenneth1, Henshall-Powell, Rhonda1, Ravani, Shraddha1, Warterts, Ray2, Arteaga, Carlos3, 1 Life Sciences Division, Berkeley, CA2 University of Utah Medical Center, Salt Lake City, UT3 Vanderbilt University, Nashville, TN
ABSTRACT-
Transforming growth factor-beta1 (TGFb) orchestrates multiple cell fate decisions in development, differentiation and disease, particularly wounding, inflammation and neoplasia. We have shown that TGFb is rapidly activated in irradiated mouse mammary gland following whole body exposure to doses as low as 0.1 Gy. To determine whether TGFb mediates cell fate in irradiated tissue, Tgfb1 null heterozygote mice were used. In wildtype mice, apoptosis increased 5-fold after exposure to a dose of 5 Gy -radiation, while in in irradiated Tgfb1 -/+ mice apoptosis was less than a third of irradiated wildtypes.. Thus TGF- genotype has a significant impact on the apoptotic response of mammary gland to radiation. Apoptosis has been shown to be p53 dependent in the mammary gland. In wildtype mice, phosphorylation of Ser-18 p53 was induced from 1 hr through 24 hr post radiation. Total p53, detected using PAb122 which is insensitive to phosphorylation status, was increased from 4 to 24 hrs post-irradiation, thus indicating a functional p53 response. Since the mammary gland is comprised of many cell types, immunofluorescence was used to determine which cells were responsive. Phosphorylated Ser-18 p53 was localized in the epithelial nuclei. However, in irradiated Tgf 1 null heterozygote mammary glands, phosphorylated Ser-18 p53 was significantly reduced in the epithelium. Since chronic depletion of TGFb in the null heterozygotes could perturb aspects of cell differentiation that in turn modify p53, pan-specific TGFb neutralizing antibodies were used to transiently deplete TGFb shortly before irradiation. Inhibition of TGFb was accompanied by reduced Ser-18 p53 phosphorylation as measured by immunofluorescence or immunoblotting. These data demonstrate that TGFb is an extracellular mediators of radiation damage involved in cellular DNA damage responses and cell fate decisions. As such, inhibition of TGFb may be useful as a countermeasure to radiation exposure. Supported by NASA Radiation Health Effects funding.
KEYWORDS: growth factor, cell fate, mammary gland, signaling